An interesting way to explain radiation exposure and risk

Science blogger Lee Falin has a potentially useful analogy for putting radiation dose and risk into perspective—treat it like currency. Part of the problem with explaining radiation is that there are multiple units of measurement in play and they're all unfamiliar to the average Joe and Jane. The numbers get confusing quickly and when numbers get confusing, most people just tune them out. "Blah blah blah blah radiation blah blah" is both an unhelpful message, and an often terrifying one.

Falin tries to get around that problem by putting radiation doses into a number system that everybody knows and uses every day—money. He starts by deciding arbitrarily that 1 sievert of exposure is worth $1000. Once you've got that established, it's easier to understand relative doses. In this system, getting $4000 all at once is a deadly dose. Most of us get $2.00-$3.00 a year in background radiation exposure. A mammogram is worth .40.

This is not a perfect method. In particular, it seems to work best for acute exposure. Falin still hasn't totally solved the problem of explaining the accumulation of radiation over time. But I think that this idea—thinking of radiation doses in terms of money—could go a long way to helping some people understand this stuff a little better. I really liked how he explained cancer risks, for instance:

What about the long term risk of cancer caused by radiation exposure? According to the EPA, an average of 2,000 out of every 10,000 adults will die from some form of cancer. If you expose everyone in that group to an extra $10.00 of radiation in one year, the number will jump to about 2,005 people.

18 Responses to “An interesting way to explain radiation exposure and risk”

Adding exposure to radioactive materials, rather than just radiation sources, probably doesn’t help the complexity picture any; but seems like an important aspect if one is interested in accident-related exposures. Something like x-ray diagnostic imaging is nice and clean and reasonably evenly distributed; but radioactive compounds can be concentrated in particular areas of the body by internal processes(like the iodine-to-the-thyroid issue) and exposure can vary wildly depending on how you are protected and what you do while in the contaminated area.

Much more vexing than exposure to an isolated radiation source, which is troublesome enough to accurately quantify…

The usual model which assumes a linear risk, with zero-dose = zero risk is wrong. It is like saying that if 10 liters of pure water taken all at once will kill one person, then if 10,000 people each drink 1 milliliter, we can expect one of them to die. It really is that stupid.

Actually, small doses likely improve health, up to a point, then the effects reverse so that one is at the same risk as with a zero dose, and only after that point is there an increased risk. It’s a J-shaped curve, with an initial dip below the baseline. The initial portion of the increasing-risk part of the graph is pretty flat, but it gets steeper the farther out one goes. On the other hand, low-level chronic exposure even at somewhat harmful levels will usually give some protection against the acute effects of very high doses later.
See: http://en.wikipedia.org/wiki/Radiation_hormesis for more.

Radiation acts very much like other toxins – it’s the dose that makes the poison, small amounts are often beneficial, and exposure usually allows tolerance to larger doses. But “radiation” isn’t one thing, and different types have different effects. Alpha-emitting isotopes that bio-accumulate and concentrate in certain tissues are very much like compound interest – but with low interest rates like a savings account, and bank fees generally more than compensating when excretion exceeds ingestion, as it almost always does.

The crucial factor is not the absolute amount of radiation, but the rate at which it is received. Doses received over minutes to hours will have many times worse effects than the same doses absorbed over a day, which in turn will be much worse than if they were absorbed over a week. The body can repair most radiation damage, and it can respond to radiation damage by increasing repair rates – sometimes to the point that it completely counteracts the damage and even works on repairing damage from non-radiation sources. But if the damage comes all at once, the repair mechanisms are overwhelmed.

It’s no trouble to drink 10 liters of water over a couple of days, but doing it all at once can be fatal.

I don’t think you can characterize radiation exposure to that of toxins per se and the water analogy isn’t helpful either; as I understand it exposure to radioactive materials cause cellular damage and their emissions”slice” DNA creating the possibility for cell death or uncontrolled reproduction (aka cancer.) Radioactive materials can build up in the body like toxic materials do, but the way they damage is different. I will be the first to admit that I don’t understand the full scope of the way the cumulative effect of radiation exposure works, but it seems to be the consensus that this also increases risk.

Radioactive hormesis is one hypothesis, but again as I understand the science it just isn’t well enough understood to make any definite claims. The body can catch some of the damage and “remediate” it, but small doses do still have the potential to inflict serious harm, it all depends on if the body recognizes and eliminates the damaged cells.

The recognized standard is the LNT, the National Academies of Sciences review in 2005 supported that position based on available scientific observations. There is still back and forth and other hypotheses may change or modify that position eventually with more scientific evidence, but for now Linear No-Threshold is the safe position.

Says official reports? 64 people died from exposure to radiation, but MAAny many reports were written predicting deaths in thousands up to 10 years from the disaster. Over 20 years passed and people studying effects of radiation still cant find higher death rates in Chernobyl ‘victims’.

WHO still publishes papers citing 230 leukemia deaths in a pool of 240K workers as direct result of the incident … forgetting to mention that its a NORMAL percentage of people getting leukemia in human population, same percentage will get it in Australia or Hawai.

I think the analogy would be easier to understand if it were put in terms of debits rather than credits, and perhaps if the numbers were multiplied by 100 or so. “If the average person [has to pay $10,000] in radiation money in a short time period, their blood chemistry will start to be affected; at around [$50,000] they’ll start to experience nausea and vomiting; and at somewhere between [$80,000 – $100,000] they’ll start to see hair loss and internal hemorrhaging. [Having to pay $400,000] or higher is typically fatal.” See what I mean? This also lets one make better sense of cumulative vs. acute exposure. If I have to pay $400,000 all at one time, I’d probably go bankrupt, but I could pay that much out over a lifetime and survive, perhaps with adverse effects on my overall financial stability – having to make a payment every month could leave me at a greater risk for adverse financial events. Similarly, 4 Sv might kill me, but the same exposure over time wouldn’t, although it might increase my cancer risk.

So the more radiation I am exposed to, the better my lifestyle will be? Comparing radiation with money is a terrible analogy.

A better analogy would be: exposure to radiation is like getting punched. A chest x-ray (0.1 mSv) is like getting punched in the chest by your kid brother: it may sting for a second, but no real damage is done. 1 Sv of radiation is like getting punched in the gut by Mike Tyson: you will likely experience internal hemorrhaging.

“Falin still hasn’t totally solved the problem of explaining the accumulation of radiation over time.”

Science in general isn’t quite sure about that. Small doses might accumulate additively. There might be a dose rate with no negative effect at all. There might even be a hormesis effect where low enough doses are beneficial.

I came up with the piggy bank. Were are all piggy banks and every time we eat a fish that has some radiation in it, get a chest xray, fly, eat drink or smoke anything contaminated and so on – it adds up in the piggy bank.

Radiation is complex; that’s how science rolls. Any simple analogy is going to be too simple. What about the continuous radiation from the phosphor in our own bones is that your budget, cash flow, overhead?

I worked at a science museum up until about a year ago, and when XKCD posted the radiation chart, I went to work converting it to dollar amounts in a very similar way. In addition, I printed stacks of fake money to represent the amounts. When I talked with guests about the big exposure events, I could drop $100,000 in $100 dollar bills in front of them and say “That’s severe poisoning. An x-ray is $4.” Got a lot of questions about cellphone radiation, too. One of my more successful demos.

Here’s the spreadsheet I based it on. It’s been a while, so I don’t remember the exact calculations I used, but like I said it’s based mostly on Randal Monroe’s work on XKCD.